ADE7761BARS-REF AD [Analog Devices], ADE7761BARS-REF Datasheet - Page 12

• Manufacturer Part Number: ADE7761BARS-REF
• Description: Energy Metering IC with On-Chip Fault and Missing Neutral Detection
• Manufacturer: AD [Analog Devices]

ADE7761B
Typical Connection Diagrams
Figure 15 shows a typical connection diagram for Channel V1.
The analog inputs are used to monitor both the phase and
neutral currents. Because of the large potential difference
between the phase and neutral, two current transformers (CTs)
must be used to provide the isolation. Note that both CTs are
referenced to analog ground (AGND); therefore, the common-
mode voltage is 0 V. The CT turn ratio and burden resistor (RB)
are selected to give a peak differential voltage of ±660 mV/gain.
Figure 16 shows two typical connections for Channel V2.
The first option uses a potential transformer (PT) to provide
complete isolation from the main voltage. In the second option,
the ADE7761B is biased around the neutral wire, and a resistor
divider is used to provide a voltage signal that is proportional to
the line voltage. Adjusting the ratio of RA and RB + VR is a
convenient way to carry out a gain calibration on the meter.
Figure 17 shows a typical connection for the MISCAL input.
The voltage reference input (REF
to set the MISCAL voltage.
IP
IN
REF
1
RB + VR = RF.
AGND
IN/OUT
Figure 16. Typical Connections for Channel V2
Figure 15. Typical Connection for Channel V1
Figure 17. Typical Connection for MISCAL
RA
CT
CT
RC
1
RB
VR
VR1
RD
1
1
RB
RB
AGND
±660mV
±660mV
±660mV
C
GAIN
GAIN
C
F
R
R
F
F
F
R
R
R
R
IN/OUT
F
F
F
F
C
C
C
F
F
T
C
F
) is used as a dc reference
MISCAL
C
C
V
V
V
V
F
F
2N
2N
2P
2P
V
V
V
V
2N
1A
1N
1B
Rev. 0 | Page 12 of 24
Adjusting the level of MISCAL to calibrate the meter in missing
neutral mode can be done by changing the ratio of RC and
RD + VR1. When the internal reference is used, the values of RC,
RD, and VR1 must be chosen to limit the current sourced by
the internal reference sourcing current to below the specified
10 μA. Therefore, because V
VR1 > 600 kΩ.
INTERNAL OSCILLATOR
The nominal internal oscillator frequency is 450 kHz when
used with the recommended R
between RCLKIN and DGND (see Figure 18).
The internal oscillator frequency is inversely proportional to the
value of this resistor. Although the internal oscillator operates
when used with an R
it is recommended that a value be chosen within the range of
the nominal value.
The output frequencies on CF, F1, and F2 are directly propor-
tional to the internal oscillator frequency; therefore, Resistor R
must have a low tolerance and low temperature drift. A low
tolerance resistor limits the variation of the internal oscillator
frequency. A small variation of the clock frequency and, conse-
quently, of the output frequencies from meter to meter contributes
to a smaller calibration range of the meter.
A low temperature drift resistor directly limits the variation of
the internal clock frequency over temperature. The stability of
the meter to external variation is then better ensured by design.
REFERENCE
ADE7761B
2.5V
Figure 18. Internal Oscillator Connection
REF
3kΩ
IN/OUT
9
OSC
resistor value between 5 kΩ and 12 kΩ,
OSCILLATOR
R
REF
INTERNAL
OSC
OSC
internal = 2.5 V, RC + RD +
14
RCLKIN
resistor value of 6.2 kΩ
17
DGND
OSC